Sand consolidation and gravel packing are two near wellbore techniques widely used for controlling the production of sand from producing wells such as oil wells, gas wells and similar boreholes. In many instances, highly porous and fragmentable sand formations surround a wellbore. Under production conditions, the sand is often displaced from its aggregated structure and carried along by the fluid flood operations to a producing well. If the sand flow is allowed to proceed unchecked, the producing wellbore soon becomes full of sand, thereby clogging the wellbore and impeding oil production. Furthermore, sand arriving at the surface site of the well erodes the production hardware.
As more and more sand is displaced from its original formation, a region of wash-out cavities surrounding the wellbore region results. As the wash-out zones become more extensive, the integrity of the wellbore is threatened and a danger of the wellbore collapsing exists.
It has therefore been the subject of extensive and intense research by the petroleum industry to develop techniques to minimize or obviate displacement of sand particles into producing well areas and prevent the formation of wash-out cavities surrounding the wellbore. One such general approach suggested by the art is to consolidate the coarse sand structures prior to fluid production. Sand consolidation techniques are aimed at cementing loose sand structures adjacent a wellbore. Such consolidation is effective to prevent breakdown of sand formation and subsequent clogging of producing wells.
In many loosely consolidated or unconsolidated formations, it is not economically or practically feasible to consider sand consolidation techniques. Also, there are many instances where substantial wash-out cavities are either initially present naturally near the wellbore or washed-out cavities form around the wellbore after prolonged use despite previous attempts at sand consolidation.
For these conditions, gravel packing techniques are often used to prevent formation sand production or further erosion and to reestablish the integrity of the wellbore periphery. Gravel packing is a secondary sand consolidation technique involving the introduction of a fluid suspension of exogenous particulate matter downhole, to fill the wash-out cavities or to "squeeze" to pack into the formation in the vicinity of the well. The term gravel is somewhat loosely applied in the art to encompass hard, rigid particulate matter ranging in size from a coarse sand to pebble size material.
Once the placement of sand and gravel has been accomplished, a slotted liner or "screen" placed as part of the production string helps hold the loose filling material and retard the upstream sand flow through the filler material during production conditions.
Present gravel pack procedures often require a filling of the casing with weighted completion fluid or drilling mud prior to perforating. Thereafter, the production casing is perforated via a casing gun with shots placed in a helical arrangement. Substantial amounts of wellbore fluid are often lost as in most instances the wellbore is in an overbalanced condition. If the well is not completely dead following the perforation operation, it is generally "killed" so the perforating tool can be pulled from the borehole. After pulling the perforating tool from the borehole, the production tubing along with a slotted liner is directed into the borehole. As a result of these operations, substantial amounts of expensive workover fluid can be lost during these operations. Because of the density, viscosity and chemical makeup of these workover fluids, damage often occurs to the permeability of a formation. Afterwards, in order to stabilize the sand in the formation, an in-casing gravel pack is generally placed within the wellbore along with additional fluids and chemicals. This results often in additional damage to the permeability of the formation. Preventing damage is made more difficult when the formation contains substantially high temperatures and salinities.
Therefore, what is needed is a gravel pack method which will minimize the permeability damage to the formation caused by workover fluids and chemicals under substantially high temperature and high salinity conditions.